Henry dbetftts



Patented Nev.- 19, 1929 HENRY memos, or LONDON, anemia MANUFACTURE OF AN mam o-Fr'ics ALnEApIc comrotmn No Drawing. Application filed ma a, 1927;. Serial so. 188,403, and in Great Britain as as, iege.

This invention relates to the production of acetic anhydride bv the pyrogenic decomposition of acetic acid. I

According to the present invention I have now found that acetic anhydride may readily be prepared by passing acetic acid vapour over or otherwise in contact with a heated catalyst or contact mass comprising one or mlpre phosphoric acids, for instance, ortho- P phosphoric' acid or mixtures of two or more of such phosphoric acids.

The reaction is preferably carried out at temperatures higher than the boiling point of acetic anhydride, for exam 1e at temperatures of from about 100 C. and preferably about 150 C. to 400 C. I

In performing the invention I- may pass acetic acid vapour over the catalyst or con: tact mass heated to the desired temperature, the phosphoric acid or acids being employed as such, or less advantageously spread upon, deposited on or mixed with porous materials such for example as pumice or kieselguhr or the like. Preferably I pass the acetic acid vapour in a stream over or through the phosphoric acid or acids, the latter being, if desired, subjected to stirring or other agitation.

The phosphoric acid or acids may, if desired, be regenerated continuously with the reaction, for example they may be caused to circulate continuously from the reaction zone through a. regeneration zone and then returned to the reaction zone. The regeneration may be effected by heating the phosphoric acid or acids to remove water bound or absorbed thereby.

Preferably I subject the reaction gases to fractional condensation immediately on their reaction zone, to separate the leaving the hot anhydride from water vapour present therein and to recover the acet c anhydride in as pure a form as possible; for example the hot reaction gases may be led up through one or more fract1onatingicolumns or apparatus preferably maintained which may be at temperatures intermediate between the boiling point of acetic anhydride and of water under the conditions obtaining,- whereby the acetic anhydride may be separated from water osphoric acid, metaphosphoric acid, pyrosired the crude reaction product vapour and, it may be, to any desired degree from any unconverted acetic acid.

If desired however the reaction ases may be caused to recirculate through t e hot reaction zone and thus constitute a com lete or continuous cycle of operations in which case the reaction gases are preferably treated to remove as far as possible the acetic anhydiide contalned therein prior to causing them to pass again throug the reaction zone; for instance the hot reaction gases may be caused to pass up through one'or more fractionating columns, whereby the acetic anhydride may be separated to-any desired degree from an unconverted acetic acid, and then led bac through the reaction zone.

' In performing the process of the present invention the system may, ifdesired, be maintained under reduced pressure or vacuum, whether or not the reaction gases are subjected to fractional condensation and whether or not the reaction gases are caused to recirculate through the reaction zone.

. The acetic anhydride may be recovered fromthe crude reaction product, any suit able way, asfor example by fractional distillation, preferably under vacuum, and if demay be distilled from dry sodium acetate. I

Ewample Acetic acid vapour generated by heating glacial acetic acid is passed in a stream over. or through ortho-phosphoric acid or molten pyrophosphoric acid heated to about 150- 400 C. and the acetic anhydride produced is separated by leading the hot reaction gases or vapours from the reaction zone upwards through one or more fractionating columns.

What I claim and desire to secure by Letters Patent is 1. Process for the manufacture of acetic A anhydride which comprises thermally decomposing acetic acid vapour in presence of at least one phosphoric acid.

2. Process for the manufacture of aceticu;

anhydride which comprises passing acetic acid vapour over a heated mass comprising at least one phosphoric acid.

Processfor the manufacture of acetic aci at least one phosphoric acid, and subjecting the reaction'vapours condensation by 3' to temperatures of from' 150 to 400 anh dride which comprises passing acetic vaPour over a mass heated to temperatures o from 150 to 400 0., said mass comprising at least one phosphoric acid.

4. Process for the manufacture of acetic anh dride which comprises passing acetic aci vapour over aheated mass comprising meta hosphoric acid. 7

5. rocess for the manufacture of acetic anh dride which comprises passing acetic aci vapour over a mass com rising metaphosphoric acid said vmass being heated to temperatures of from 150 to 400 C.

6. Process for the manufacture of acetic anhydride which comprises passing acetic acid vapour over a heated mass comprising at least one phosphoric -agid, and sub ecting the reaction vapours to fra tional condensation.

7. Process for the anh dride which comprises" aci vapour over a heated mass comprising to fractional condensation by leading said reaction vapours u wards through at umn maintained at temperatures intermediate between'the boiling points (under the conditions of pressure obtaining) of acetic anhydride and of water.

8. Process for the manufacture of acetic anhydride which comprises passing acetic acid vapour over a mass comprising at least one phosphoric acid, said mass beingieatedd an subjecting the reaction vapours to fractional condensation. I

' 9. Process for the manufacture of acetic anh dride which comprises passing acetic aci vapour over a mass comprising at least one phosphoric acid, said mass being heated to temperatures of from 150 to 400 0. and subjecting the reaction vapours to fractional leading said reaction, vapours upwards throughat least one fractionating column maintained at temperatures intermediate between the boiling points (under the conditions of. ressure obtaining) of acetic anhydride and 0 water.

10. Process for the manufacture of acetic anh dride which comprises passing acetic aci vapour over a heated mass consisting of at least one phosphoric acid spread upon a carrier.

anh 'dride which comprises passing acetic aci vapour over a heated mass conslsting of at least one phosphoric acid spread upon pumice.

'mg sai manufacture of acetic passlng acetic least one fractionating co 4 11. Process for the manufacture of acetic.

generation zone wherein said mass is heated to remove absorbed water, (1 mass to the reaction In testimony whereof I have scribed my name.

12. Process for the manufacture of acetic anhydride which comprises passing acetic acid vapour over a heated mass comprising at least one phosphoric acid, and continuously regenerating said mass by causing said mass to circulate from the reaction zone to a rezone.

7 HE NRY DREYFUS.

and then returnhereunto sub- 

